Light-emitting diode and application therefor

ABSTRACT

A light-emitting diode is provided to include: a transparent substrate having a first surface, a second surface, and a side surface; a first conductive semiconductor layer positioned on the first surface of the transparent substrate; a second conductive semiconductor layer positioned on the first conductive semiconductor layer; an active layer positioned between the first conductive semiconductor layer and the second conductive semiconductor layer; a first pad electrically connected to the first conductive semiconductor layer; and a second pad electrically connected to the second conductive semiconductor layer, wherein the transparent substrate is configured to discharge light generated by the active layer through the second surface of the transparent substrate, and the light-emitting diode has a beam angle of at least 140 degrees or more. Accordingly, a light-emitting diode suitable for a backlight unit or a surface lighting apparatus can be provided.

PRIORITY CLAIMS AND CROSS-REFERENCES TO RELATED APPLICATIONS

This patent document is a continuation of U.S. patent application Ser.No. 14/733,787 filed Jun. 8, 2015, which is a continuation-in-part of,and claims priority and the benefits of, a Patent Cooperation Treaty(PCT) application number PCT/KR2013/009395, entitled “LIGHT-EMITTINGDIODE AND APPLICATION THEREFOR” and filed with the Korean IntellectualProperty Office (KIPO) on Oct. 22, 2013, which further claims prioritiesand the benefits of Korean patent application number 10-2013-0011453entitled “LIGHT-EMITTING DIODE AND APPLICATION THEREFOR” filed with KIPOon Jan. 31, 2013, Korean patent application number 10-2012-0155783entitled “LIGHT-EMITTING DIODE AND APPLICATION THEREFOR” filed with KIPOon Dec. 28, 2012, and Korean patent application number 10-2012-0140991entitled “LIGHT-EMITTING DIODE AND APPLICATION THEREFOR” filed with KIPOon Dec. 6, 2012. The contents of each application are incorporated byreference in their entirety.

TECHNICAL FIELD

This patent document relates to a light emitting diode and applicationthereof and, more particularly, to a flip-chip type light emitting diodehaving improved beam angle and application thereof.

BACKGROUND

Gallium nitride (GaN)-based light emitting diodes (LEDs) have beenbroadly used in a wide range of applications including full color LEDdisplays, LED traffic signboards, backlight units, lighting devices, andthe like.

Generally, a GaN-based light emitting diode is formed by growingepitaxial layers on a substrate such as a sapphire substrate, andincludes an n-type semiconductor layer, a p-type semiconductor layer andan active layer interposed therebetween. On the other hand, anN-electrode pad is formed on the n-type semiconductor layer and aP-electrode pad is formed on the p-type semiconductor layer. The lightemitting diode is electrically connected to an external power sourcethrough the electrode pads and operated thereby. Here, electric currentflows from the P-electrode pad to the N-electrode pad through thesemiconductor layers.

On the other hand, a flip-chip type light emitting diode is used toprevent light loss by the P-electrode pad while improving heatdissipation efficiency. The flip-chip type light emitting diode emitslight through a growth substrate and thus can reduce light loss by theP-electrode pad, as compared with a vertical type light emitting diodethat emits light through epitaxial layers thereof. Furthermore, alateral type light emitting diode is configured to discharge heatthrough a growth substrate such as a sapphire substrate and thus has lowheat dissipation efficiency. On the contrary, the flip-chip type lightemitting diode discharges heat through the electrode pads and thus hashigh heat dissipation efficiency.

Furthermore, a vertical type light emitting diode is fabricated byremoving the growth substrate such as a sapphire substrate fromepitaxial layers in order to improve light extraction efficiency.Particularly, the vertical type light emitting diode can prevent lightloss due to total internal reflection by texturing an exposed surface ofthe semiconductor layer.

On the other hand, in a specific application, particularly, in anapplication requiring irradiation of light over a wide area as in abacklight unit or a sheet-lighting apparatus, a beam angle of light isan important issue.

Generally, a conventional flip-chip type light emitting diode has a beamangle of about 120°, and a typical vertical type light emitting diodehas a smaller beam angle than about 120° due to surface texturing.Accordingly, in the related art, a molding member or a separatesecondary lens is used in order to increase a beam angle of light at apackage level.

On the other hand, a lighting apparatus such as an LED fluorescent lampmay require an LED having different beam angles according to directions.When a plurality of LEDs is mounted inside a lighting apparatus of anelongated fluorescent lamp shape, it is advantageous that the LEDs havelarge beam angles in a direction orthogonal to a longitudinal directionof the fluorescent lamp.

SUMMARY

Some implementations of the disclosed technology provide a flip-chiptype light emitting diode suitable for a backlight unit or asheet-lighting apparatus, and application thereof.

Some implementations of the disclosed technology provide a flip-chiptype light emitting diode that has improved light extraction efficiencythrough improvement in reflectivity.

Some implementations of the disclosed technology provide a flip-chiptype light emitting diode that has improved current spreadingperformance.

Some implementations of the disclosed technology provide a lightemitting diode that has different beam angles of light according todirections, and a lighting apparatus including the same.

Some implementations of the disclosed technology provide a flip-chiptype light emitting diode having improved luminous efficacy, and alighting apparatus including the same.

In one aspect, a light emitting diode is provided to include: atransparent substrate having a first surface, a second surface and aside surface connecting the first surface and the second surface; afirst conductive type semiconductor layer placed over the first surfaceof the transparent substrate; a second conductive type semiconductorlayer placed over the first conductive type semiconductor layer; anactive layer placed between the first conductive type semiconductorlayer and the second conductive type semiconductor layer; a first padelectrically connected to the first conductive type semiconductor layer;and a second pad electrically connected to the second conductive typesemiconductor layer, wherein the transparent substrate is configured todischarge light generated in the active layer through the second surfaceof the transparent substrate. Further, the light emitting diode has abeam angle of 140° or more.

Unlike a typical light emitting diode, the light emitting diodeaccording to embodiments of the disclosed technology has a relativelywide beam angle of 140° or more without using a lens-shaped moldingmember or a secondary lens. Thus, the light emitting diode according tothe embodiments of the disclosed technology is suitable for a lightingapparatus including a sheet-lighting apparatus. The light emitting diodeaccording to the embodiments of the disclosed technology may be directlyused in various applications without a separate packaging process.Furthermore, the light emitting diode may be used without a secondarylens or may be used together with the secondary lens after being coupledthereto.

In some implementations, the light emitting diode may further include aconformal coating layer covering the second surface of the transparentsubstrate to enable the light emitted through the second surface todischarge through the conformal coating layer. The conformal coatinglayer may contain a phosphor and thus can convert a wavelength of atleast part of light generated in the active layer.

In some implementations, a total thickness of the transparent substrateand the conformal coating layer may range from 225 μm to 600 μm. In someimplementations, the transparent substrate may have a thickness of 150μm to 400 μm. In some implementations, the conformal coating may have athickness of 20 μm to 200 μm.

In some implementations, the transparent substrate may have a thicknessof 225 μm to 400 μm. As the transparent substrate has a thickness of 225μm to 400 μm, it is possible to provide a flip-chip type light emittingdiode having a beam angle of 140° or more regardless of the presence ofthe conformal coating layer. If the thickness of the transparentsubstrate exceeds 400 μm, it is difficult to divide the substrate intoindividual light emitting diode chips.

In some implementations, the active layer and the second conductive typesemiconductor layer are patterned to form a plurality of mesas that areseparated from one another over the first conductive type semiconductorlayer.

In some implementations, the light emitting diode may further include:reflective electrodes respectively placed over the plurality of mesasand forming ohmic contacts with the second conductive type semiconductorlayer; and a current spreading layer placed over the plurality of mesasand the first conductive type semiconductor layer to form openings inupper regions of the plurality of mesas while exposing the reflectiveelectrodes, the current spreading layer forming ohmic contacts with thefirst conductive type semiconductor layer and being insulated from theplurality of mesas, wherein the first pad may be electrically connectedto the current spreading layer and the second pad may be electricallyconnected to the reflective electrodes through the openings.

Since the current spreading layer covers the plurality of mesas and thefirst conductive type semiconductor layer, the light emitting diode hasimproved current spreading performance through the current spreadinglayer.

In some implementations, the first conductive type semiconductor layermay be continuous. In some implementations, the plurality of mesas mayhave an elongated shape extending in one direction and may be disposedparallel to each other. In some implementations, the openings of thecurrent spreading layer may be placed to be biased towards the same endsof the plurality of mesas. Thus, a pad connecting the reflectiveelectrodes exposed through the openings of the current spreading layerto each other can be easily formed.

In some implementations, the current spreading layer may include areflective metal such as Al. With this structure, it is possible toprovide light reflection by the current spreading layer in addition tolight reflection by the reflective electrodes, whereby light travelingthrough sidewalls of the plurality of mesas and the first conductivetype semiconductor layer can be reflected thereby.

In some implementations, each of the reflective electrodes may include areflective metal layer and a barrier metal layer, the barrier metallayer may cover an upper surface and a side surface of the reflectivemetal layer. With this structure, it is possible to preventdeterioration of the reflective metal layer by preventing the reflectivemetal layer from being exposed to the outside.

In some implementations, the light emitting diode may further include anupper insulation layer covering at least part of the current spreadinglayer and including or placed to form openings exposing the reflectiveelectrodes; and the second pad is electrically connected to thereflective electrodes exposed through the openings of the upperinsulation layer.

In some implementations, the first pad and the second pad may have thesame shape and the same size, thereby facilitating flip-chip bonding.

In some implementations, the light emitting diode may further include alower insulation layer placed between the plurality of mesas and thecurrent spreading layer and insulating the current spreading layer fromthe plurality of mesas, wherein the lower insulation layer may includeor be placed to form respective openings in the upper regions of themesas that expose the reflective electrodes.

In some implementations, the openings of the current spreading layer mayhave a greater width than the openings of the lower insulation layer soas to allow the opening of the lower insulation layer to be completelyexposed through the openings of the current spreading layer. In someimplementations, sidewalls of the current spreading layer may be placedon the lower insulation layer. In some implementations, the lightemitting diode may further include an upper insulation layer covering atleast part of the current spreading layer and including or placed toform openings exposing the reflective electrodes. The upper insulationlayer may cover sidewalls of the openings of the current spreadinglayer.

In some implementations, the lower insulation layer may be or include areflective dielectric layer, for example, a distributed Bragg reflector(DBR).

In another aspect, a light emitting diode is provided to include: atransparent substrate having a first surface and a second surface afirst conductive type semiconductor layer placed over the first surfaceof the transparent substrate; a second conductive type semiconductorlayer placed over the first conductive type semiconductor layer; anactive layer placed between the first conductive type semiconductorlayer and the second conductive type semiconductor layer; a first padelectrically connected to the first conductive type semiconductor layer;and a second pad electrically connected to the second conductive typesemiconductor layer, wherein the transparent substrate is configured toenable light generated in the active layer to discharge through thetransparent substrate via the second surface of the transparentsubstrate, and the transparent substrate has a thickness of 225 μm to400 μm.

In another aspect, a light emitting diode is provided to include: atransparent substrate; a first conductive type semiconductor layerplaced over the first surface of the transparent substrate; a secondconductive type semiconductor layer placed over the first conductivetype semiconductor layer; an active layer placed between the firstconductive type semiconductor layer and the second conductive typesemiconductor layer; a first pad electrically connected to the firstconductive type semiconductor layer; a second pad electrically connectedto the second conductive type semiconductor layer; and a conformalcoating layer covering the transparent substrate, wherein thetransparent substrate and the conformal coating layer are arranged toenable light generated in the active layer to discharge through theconformal coating layer, and a total thickness of the transparentsubstrate and the conformal coating may range from 225 μm to 600 μm.

In some implementations, the transparent substrate may have a thicknessof 150 μm to 400 μm. In some implementations, the conformal coating mayhave a thickness of 20 μm to 200 μm.

In another aspect, a lighting module is provided to include at least oneof light emitting diode comprising: a transparent substrate having afirst surface and a second surface; a first conductive typesemiconductor layer placed over the first surface of the transparentsubstrate; a second conductive type semiconductor layer placed over thefirst conductive type semiconductor layer; an active layer placedbetween the first conductive type semiconductor layer and the secondconductive type semiconductor layer; a first pad electrically connectedto the first conductive type semiconductor layer; and a second padelectrically connected to the second conductive type semiconductorlayer, wherein the transparent substrate is placed to enable lightgenerated in the active layer to discharge through the second surface ofthe transparent substrate. Further, the at least one of the lightemitting diodes has a beam angle of 140° or more.

In some implementations, the transparent substrate has a thickness of225 μm to 400 μm.

In some implementations, the at least one of the light emitting diodesmay further include a conformal coating layer covering the secondsurface of the transparent substrate and a total thickness of thetransparent substrate and the conformal coating layer may range from 225μm to 600 μm. In some implementations, the conformal coating may have athickness of 20 μm to 200 μm.

In some implementations, the active layer and the second conductive typesemiconductor layer are patterned to form a plurality of mesas over thefirst conductive type semiconductor layer, the plurality of mesas beingseparated from one another.

In some implementations, the at least one light emitting diode furthercomprises: reflective electrodes placed over the plurality of mesas andforming ohmic contact with the second conductive type semiconductorlayer; and a current spreading layer placed over the plurality of mesasand the first conductive type semiconductor layer to form respectiveopenings in upper regions of the plurality of mesas and exposing thereflective electrodes, the current spreading layer forming ohmiccontacts with the first conductive type semiconductor layer and beinginsulated from the plurality of mesas, wherein the first pad iselectrically connected to the current spreading layer and the second padis electrically connected to the reflective electrodes through theopenings.

In some implementations, the at least one light emitting diode furthercomprises a lower insulation layer covering at least a portion of theplurality of mesas and at least a portion of the first conductive typesemiconductor layer.

In another aspect, a lighting apparatus is provided to include alighting module that includes a plurality of light emitting diodes atleast one light emitting diode. The at least one light emitting diodeincludes: a transparent substrate; a first conductive type semiconductorlayer placed over the transparent substrate; a second conductive typesemiconductor layer placed over the first conductive type semiconductorlayer; an active layer placed between the first conductive typesemiconductor layer and the second conductive type semiconductor layer;a first pad electrically connected to the first conductive typesemiconductor layer; and a second pad electrically connected to thesecond conductive type semiconductor layer, wherein the transparentsubstrate is placed to enable light generated in the active layer todischarge through the transparent substrate, and the at least one lightemitting diode has a beam angle of 140° or more.

In some implementations, the transparent substrate has a thickness of225 μm to 400 μm. In some implementations, the at least one lightemitting diode further comprises a conformal coating layer placed overthe transparent substrate, and a total thickness of the transparentsubstrate and the conformal coating ranges from 225 μm to 600 μm. Insome implementations, the active layer and the second conductive typesemiconductor layer are patterned to form a plurality of separate mesasover the first conductive type semiconductor layer. In someimplementations, at least one of the plurality of separate mesas extendto an edge of the first conductive type semiconductor layer.

In another aspect, a backlight unit is provided to include at least onelight emitting diode comprising: a transparent substrate having a firstsurface and a second surface; a first conductive type semiconductorlayer placed over the first surface of the transparent substrate; asecond conductive type semiconductor layer placed over the firstconductive type semiconductor layer; an active layer placed between thefirst conductive type semiconductor layer and the second conductive typesemiconductor layer; a first pad electrically connected to the firstconductive type semiconductor layer; and a second pad electricallyconnected to the second conductive type semiconductor layer, wherein thetransparent substrate is placed to enable light generated in the activelayer is discharged through the transparent substrate via the secondsurface of the transparent substrate. Further, the at least one lightemitting diode has a beam angle of 140° or more.

In some implementations, the transparent substrate may have a thicknessof 225 μm to 400 μm.

In some implementations, the at least one light emitting diode mayfurther include a conformal coating layer covering the second surface ofthe transparent substrate, and a total thickness of the transparentsubstrate and the conformal coating may range from 225 μm to 600 μm. Insome implementations, the conformal coating may have a thickness of 20μm to 200 μm.

In some implementations, the active layer and the second conductive typesemiconductor layer are patterned to form a plurality of mesas over thefirst conductive type semiconductor layer, the plurality of mesas beingseparated from one another. In some implementations, the at least onelight emitting diode further comprises: reflective electrodes placedover the plurality of mesas and forming ohmic contacts with the secondconductive type semiconductor layer; and a current spreading layercovering the plurality of mesas and the first conductive typesemiconductor layer and placed to form respective openings in upperregions of the plurality of mesas while exposing the reflectiveelectrodes, the current spreading layer forming ohmic contacts with thefirst conductive type semiconductor layer and being insulated from theplurality of mesas, wherein the first pad is electrically connected tothe current spreading layer and the second pad is electrically connectedto the reflective electrodes through the openings.

In some implementations, the at least one light emitting diode furthercomprises a lower insulation layer covering at least a portion of theplurality of mesas and at least a portion of the first conductive typesemiconductor layer. In some implementations, at least one of theplurality of mesas extends to an edge of the first conductive typesemiconductor layer.

In another aspect, a light emitting diode is provided to include: atransparent substrate; a first conductive type semiconductor layerplaced over the first surface of the transparent substrate; a secondconductive type semiconductor layer placed over the first conductivetype semiconductor layer; an active layer placed between the firstconductive type semiconductor layer and the second conductive typesemiconductor layer; a first pad electrically connected to the firstconductive type semiconductor layer; and a second pad electricallyconnected to the second conductive type semiconductor layer, wherein thetransparent substrate is placed to enable light generated in the activelayer to discharge through the transparent substrate and the transparentsubstrate has a polygonal shape including at least one acute angle.

Since the amount of light discharged near the acute portion increases,the light emitting diode has improved light extraction efficiency andallows adjustment of beam angles thereof. Accordingly, it is possible toprovide a light emitting diode having different beam angles according todirections.

In some implementations, the transparent substrate may have a thicknessof 100 μm to 400 μm. In some implementations, the polygonal shapeincludes a triangular shape, a parallelogram shape or a pentagonalshape. In some implementations, the transparent substrate may be orinclude a sapphire substrate. In some implementations, the polygonalshape of the transparent substrate includes a parallelogram shape and aside surface of the transparent substrate includes m-planes. Since theside surface of the transparent substrate includes en-planes, waferscribing may be performed along a crystal plane of the group ofm-planes, thereby preventing damage such as chipping during division ofthe substrate into individual light emitting diodes.

In some implementations, the light emitting diode may further include areflective electrode placed over the second conductive typesemiconductor layer and reflecting light generated in the active layer.In some implementations, the light emitting diode allows light to bereflected by the reflective electrode, thereby improving luminousefficacy.

In some implementations, the active layer and the second conductive typesemiconductor layer may be placed within the first conductive typesemiconductor layer such that an upper surface of the first conductivetype semiconductor layer is exposed along edges of the substrate.

In some implementation, the light emitting diode may further include acurrent spreading layer connecting the first pad to the first conductivetype semiconductor layer, and the first pad and the second pad may beplaced above the second conductive type semiconductor layer. Thisstructure can reduce a height difference between the first pad and thesecond pad, thereby facilitating flip-chip bonding.

In some implementations, the current spreading layer may include areflective metal. In the light emitting diode, light is reflected by thereflective electrode and the current spreading layer, thereby furtherimproving luminous efficacy of the light emitting diode.

In some implementations, the light emitting diode may further include alower insulation layer insulating the current spreading layer from thereflective electrode, the lower insulation layer placed to form openingsexposing the first conductive type semiconductor layer, wherein thecurrent spreading layer may be connected to the first conductive typesemiconductor layer through the openings of the lower insulation layer.

In some implementations, the polygonal shape has at least one obtuseangle and the lower insulating layer is placed to form the openings inan elongated shape along the edges of the transparent substrate suchthat the openings are farther separated from one another around the atleast one acute angle portion than around the at least one obtuse angleportion. With this structure, the light emitting diode can preventcurrent crowding at the acute angle portion.

In some implementations, the lower insulating layer is placed to formthe openings that include a plurality of holes separated from oneanother along the edges of the transparent substrate and a distancebetween the holes may increase around the at least one acute angleportion. With this structure, it is possible to relieve current crowdingat the acute angle portion.

In some implementations, the first surface has a greater area than thesecond surface. The first surface having a great area than the secondsurface further improves light extraction efficiency.

In some implementations, the light emitting diode may further include aconformal coating covering the second surface of the substrate. In someimplementations, a total thickness of the transparent substrate and theconformal coating may range from 225 μm to 600 μm, whereby the lightemitting diode has increased beam angle of light.

In another aspect, a lighting apparatus is provided to include at leastone light emitting diode including: a transparent substrate having afirst surface and a second surface; a first conductive typesemiconductor layer placed over the first surface of the transparentsubstrate; a second conductive type semiconductor layer placed over thefirst conductive type semiconductor layer; an active layer placedbetween the first conductive type semiconductor layer and the secondconductive type semiconductor layer; a first pad electrically connectedto the first conductive type semiconductor layer; and a second padelectrically connected to the second conductive type semiconductorlayer, wherein the transparent substrate is placed to enable lightgenerated in the active layer is discharged through the transparentsubstrate via the second surface of the transparent substrate, and thetransparent substrate has a polygonal shape including at least one acuteangle.

In some implementations, the transparent substrate has a thickness of100 μm to 400 μm. In some implementations, the polygonal shape includesa triangular shape, a parallelogram shape or a pentagonal shape. In someimplementations, the polygonal shape of the transparent substrate hasincludes a parallelogram shape and a side surface of the transparentsubstrate includes en-planes. In some implementations, the at least onelight emitting diode further comprises a conformal coating covering thesecond surface of the transparent substrate, and a total thickness ofthe transparent substrate and the conformal coating ranges from 225 μmto 600 μm.

In another aspect, a light emitting diode is provided to include: asubstrate having a first surface and a second surface opposite to thefirst surface; a first conductive type semiconductor layer placed overthe first surface of the substrate; a mesa including an active layer anda second conductive type semiconductor layer sequentially stacked overthe first conductive type semiconductor layer, the mesa having apolygonal shape including an acute angle and an obtuse angle andexposing at least a portion of the first conductive type semiconductorlayer; a lower insulation layer covering the mesa and placed to form aplurality of first openings exposing the first conductive typesemiconductor layer and a second opening exposing the second conductivetype semiconductor layer; a first pad electrically connected to thefirst conductive type semiconductor layer through the first openings;and a second pad electrically connected to the second conductive typesemiconductor layer through the second opening, wherein a distancebetween the first openings near the acute angle of the mesa is greaterthan a distance between the first openings near the obtuse angle of themesa. With this structure, the light emitting diode can prevent currentcrowding.

In some implementations, a distance between the first openings near theacute angle of the mesa is greater than or equal to a current spreadinglength, and a distance between the first openings near the obtuse angleis less than or equal to the current spreading length.

According to some implementations of the disclosed technology, theflip-chip type light emitting diode has a relatively wide beam angle oflight. Accordingly, the flip-chip type light emitting diode may besuitably used in a backlight unit or a sheet-lighting apparatus. Forexample, in arrangement of light emitting diodes having a wide beamangle, it is possible to reduce the number of light emitting diodes orto achieve a slim structure of the backlight unit or the lightingmodule.

According to embodiments of the disclosed technology, the flip-chip typelight emitting diode has improved light extraction efficiency throughimprovement in reflectivity, and has improved current spreadingperformance.

According to embodiments of the disclosed technology, the flip-chip typelight emitting diode adopts a substrate including at least one acuteangle portion, thereby improving luminous efficacy while exhibitingdifferent beam angles of light according to directions. Further, alighting apparatus employs such a light emitting diode, thereby enablingillumination of a wide area while reducing light loss.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1(a) through 5(b) are views illustrating an exemplary method offabricating a light emitting diode according to one embodiment of thedisclosed technology, in which (a) shows a plan view and (b) shows asectional view taken along line A-A.

FIG. 6 is a plan view of an exemplary modification of a mesa structure.

FIG. 7 is a sectional view of an exemplary light emitting diodeaccording to one embodiment of the disclosed technology.

FIG. 8 is a sectional view of an exemplary light emitting diodeaccording to another embodiment of the disclosed technology.

FIGS. 9 to 12 are graphs depicting beam angle characteristics of lightemitting diodes depending on thickness of substrates.

FIG. 13 is a graph depicting a relationship between beam angle andsubstrate thickness of light emitting diodes.

FIGS. 14 to 17 are graphs depicting beam angle characteristics of lightemitting diodes each having a conformal coating depending on thicknessof substrates.

FIG. 18 is a graph depicting a relationship between beam angle andsubstrate thickness of light emitting diodes each having a conformalcoating.

FIGS. 19(a) through 19(c) show schematic sectional views of a lightemitting diode module employing typical light emitting diodes and lightemitting diode modules employing light emitting diodes according to oneimplementation of the disclosed technology.

FIG. 20(a) through FIG. 24(b) are views illustrating a method offabricating a light emitting diode according to one embodiment of thedisclosed technology.

FIG. 25 shows an exemplary arrangement of a plurality of holes exposingthe first conductive type semiconductor layer along the edges of thesubstrate.

FIG. 26 shows an exemplary structure of a light emitting diode accordingto one embodiment of the disclosed technology.

FIG. 27 shows an exemplary conformal coating.

FIGS. 28(a) to 28(b) show schematic plan views illustrating lightextraction characteristics depending on the shape of a substrate.

FIG. 29 is graph depicting beam angles of a flip-chip type lightemitting diode fabricated by a typical method and a flip-chip type lightemitting diode fabricated by a method according to one embodiment of thedisclosed technology.

DETAILED DESCRIPTION

Hereinafter, various implementations of the disclosed technology will bedescribed in more detail with reference to the accompanying drawings.The following embodiments are provided by way of example so as tofacilitate the understanding of the various implementations of thedisclosed technology. Accordingly, the disclosed technology is notlimited to the embodiments disclosed herein and can also be implementedin various different forms. In the drawings, certain aspects such aswidths, lengths, thicknesses, and the like of elements may beexaggerated for clarity and descriptive purposes. Throughout thespecification, like reference numerals denote like elements having thesame or similar functions.

First, a method of fabricating a light emitting diode will be describedto aid in understanding of the structure of a flip-chip type lightemitting diode according to one embodiment of the disclosed technology.

FIG. 1(a) through FIG. 5(b) are views illustrating a method offabricating a light emitting diode according to one embodiment of thedisclosed technology, in which (a) shows a plan view and (b) shows asectional view taken along line A-A.

First, referring to FIGS. 1(a) and 1(b), a first conductive typesemiconductor layer 23 is formed on a substrate 21, and an active layer25 and a second conductive type semiconductor layer 27 are placed on thefirst conductive type semiconductor layer 23. The substrate 21 is orincludes a substrate for growth of GaN-based semiconductor layers andmay be or include, for example, a sapphire substrate, a silicon carbidesubstrate, a gallium nitride substrate, an indium gallium nitridesubstrate, an aluminum gallium nitride substrate, an aluminum nitridesubstrate, a gallium oxide substrate, and the like. In someimplementations, the substrate 21 may be or include a sapphiresubstrate.

The first conductive type semiconductor layer 23 may be or include anitride-based semiconductor layer doped with n-type impurities. In oneembodiment, the first conductive type semiconductor layer 23 may be orinclude an In_(x)Al_(y)Ga_(1-x-y)N layer (0≤x≤1, 0≤y≤1, 0≤x+y≤1) dopedwith Si. For example, the first conductive type semiconductor layer 23may be or include a Si-doped GaN layer. The second conductive typesemiconductor layer 27 may be or include a nitride-based semiconductorlayer doped with p-type impurities. In one embodiment, the secondconductive type semiconductor layer 27 may be or include anIn_(x)Al_(y)Ga_(1-x-y)N layer (0≤x≤1, 0≤y≤1, 0≤x+y≤1) doped with Mg orZn. For example, the second conductive type semiconductor layer 27 maybe or include a Mg-doped GaN layer. The active layer 25 may include awell layer including In_(x)Al_(y)Ga_(1-x-y)N (0≤x≤1, 0≤y≤1, 0≤x+y≤1) andmay have a single quantum well structure or a multi-quantum wellstructure. In one embodiment, the active layer 25 may have a singlequantum well structure including an InGaN, GaN or AlGaN layer, or amulti-quantum well structure including InGaN/GaN layers, GaN/AlGaNlayers, or AlGaN/AlGaN layers.

The first conductive type semiconductor layer 23, the active layer 25and the second conductive type semiconductor layer 27 may be formed bymetal organic chemical vapor deposition (MOCVD) or molecular beamepitaxy (MBE).

A plurality of mesas M may be formed on the first conductive typesemiconductor layer 23 to be separated from each other, and each of themesas M may include the active layer 25 and the second conductive typesemiconductor layer 27. The active layer 25 is placed between the firstconductive type semiconductor layer 23 and the second conductive typesemiconductor layer 27. On the other hand, a reflective electrode 30 isplaced on each of the mesas M.

The plural mesas M may be formed by growing epitaxial layers includingthe first conductive type semiconductor layer 23, the active layer 25and the second conductive type semiconductor layer 27 on the firstsurface of the substrate 21 through metal organic chemical vapordeposition or the like, followed by patterning the second conductivetype semiconductor layer 27 and the active layer 25 so as to expose thefirst conductive type semiconductor layer 23. The plural mesas M may beformed to have inclined side surfaces using photoresist reflowtechnology. The inclined profile of the side surfaces of the mesas Mimproves extraction efficiency of light generated in the active layer25.

As shown, the plural mesas M may have an elongated shape extending inone direction and be disposed parallel to each other. Such a shapesimplifies formation of the plural mesas M having the same shape in aplurality of chip areas on the substrate 21.

On the other hand, the reflective electrodes 30 may be formed on therespective mesas M after formation of the plural mesas M, without beinglimited thereto. Alternatively, the reflective electrodes 30 may beformed on the second conductive type semiconductor layer 27 beforeformation of the mesas M after growing the second conductive typesemiconductor layer 27. The reflective electrodes 30 cover most regionsof upper surfaces of the mesas M and have substantially the same shapeas the shape of the mesas M in plan view.

The reflective electrode 30 includes a reflective layer 28 and mayfurther include a barrier layer 29. The barrier layer 29 may cover anupper surface and a side surface of the reflective layer 28. Forexample, the barrier layer 29 may be formed to cover the upper and sidesurfaces of the reflective layer 28 by forming a pattern of thereflective layer 28 and forming the barrier layer 29 on the patternedreflective layer 28. For example, the reflective layer 28 may be formedby deposition and patterning of layers including Ag, Ag alloy, Ni/Ag,NiZn/Ag, or TiO/Ag layers. On the other hand, the barrier layer 29 maybe formed to include Ni, Cr, Ti, Pt or combinations thereof and preventsdiffusion or contamination of metallic materials in the reflective layer28.

After forming the plural mesas M, an edge of the first conductive typesemiconductor layer 23 may also be etched. As a result, an upper surfaceof the substrate 21 can be exposed. The first conductive typesemiconductor layer 23 may also be formed to have an inclined sidesurface.

As shown in FIGS. 1(a) and 1(b), the plurality of mesas M may be placedinside the first conductive type semiconductor layer 23. For example,the plurality of mesas M may be placed in island shapes within an upperregion of the first conductive type semiconductor layer 23.Alternatively, the mesas M may extend in one direction to reach edges ofthe upper surface of the first conductive type semiconductor layer 23,as shown in FIG. 6. For example, in one direction, the edges of lowersurfaces of the plurality of mesas M may coincide with the edges of thefirst conductive type semiconductor layer 23. With this structure, theupper surface of the first conductive type semiconductor layer 23 ispartitioned by the plurality of mesas M.

Referring to FIGS. 2(a) and 2(b), a lower insulation layer 31 is formedto cover the plurality of mesas M and the first conductive typesemiconductor layer 23. The lower insulation layer 31 includes or isplaced to form openings 31 a and 31 b to allow electrical connection tothe first conductive-type semiconductor layer 23 and the secondconductive-type semiconductor layer 27. For example, the lowerinsulation layer 31 may include or be placed to form openings 31 a whichexpose the first conductive-type semiconductor layer 23 and openings 31b which expose the reflective electrodes 30.

The openings 31 a may be placed between the mesas M and near edges ofthe substrate 21, and may have an elongated shape extending along themesas M. On the other hand, the openings 31 b are placed in upperregions of the mesas M to be located towards the one end of the mesas.

The lower insulation layer 31 may be formed to include oxides such asSiO₂, nitrides such as SiNx, or insulation materials such as MgF₂ bychemical vapor deposition (CVD) or the like. The lower insulation layer31 may be composed of a single layer or multiple layers. In addition,the lower insulation layer 31 may be formed as a distributed Braggreflector (DBR) in which low refractive material layers and highrefractive material layers are alternately stacked one above another.For example, an insulation reflective layer having high reflectivity maybe formed by stacking, for example, SiO₂/TiO₂ layers or SiO₂/Nb₂O₅layers.

Referring to FIGS. 3(a) and 3(b), a current spreading layer 33 is formedon the lower insulation layer 31. The current spreading layer 33 coversthe plurality of mesas M and the first conductive-type semiconductorlayer 23. In addition, the current spreading layer 33 includes or isplaced to form openings 33 a, which are respectively placed in the upperregions of the mesas M and expose the reflective electrodes 30. Thecurrent spreading layer 33 may form ohmic contacts with the firstconductive-type semiconductor layer 23 through the openings 31 a of thelower insulation layer 31. The current spreading layer 33 is insulatedfrom the plurality of mesas M and the reflective electrodes 30 by thelower insulation layer 31.

Each of the openings 33 a of the current spreading layer 33 has agreater area than the openings 31 b of the lower insulation layer 31 toprevent the current spreading layer 33 from being connected to thereflective electrodes 30. Thus, the openings 33 a have sidewalls placedon the lower insulation layer 31.

The current spreading layer 33 is formed substantially over the entiretyof the upper surface of the substrate 31 excluding the openings 33 a.Accordingly, current can easily spread through the current spreadinglayer 33. The current spreading layer 33 may include a highly reflectivemetal layer such as an Al layer, and the highly reflective metal layermay be formed on a bonding layer such as a Ti, Cr or Ni layer. Inaddition, a protective layer having a single layer or composite layerstructure including Ni, Cr, Au, and the like may be formed on the highlyreflective metal layer. The current spreading layer 33 may have amultilayer structure including, for example, Ti/Al/Ti/Ni/Au.

Referring to FIGS. 4(a) and 4(b), an upper insulation layer 35 is formedon the current spreading layer 33. The upper insulation layer 35includes or is placed to form an opening 35 a which exposes the currentspreading layer 33, and openings 35 b which expose the reflectiveelectrodes 30. The opening 35 a may have an elongated shape in aperpendicular direction with respect to the longitudinal direction ofthe mesas M, and has a greater area than the openings 35 b. The openings35 b expose the reflective electrodes 30, which are exposed through theopenings 33 a of the current spreading layer 33 and the openings 31 b ofthe lower insulation layer 31. The openings 35 b have a narrower areathan the openings 33 a of the current spreading layer 33 and a greaterarea than the openings 31 b of the lower insulation layer 31.Accordingly, the sidewalls of the openings 33 a of the current spreadinglayer 33 may be covered by the upper insulation layer 35.

The upper insulation layer 35 may be formed to include an oxideinsulation layer, a nitride insulation layer, or a polymer such aspolyimide, Teflon, Parylene, or the like.

Referring to FIGS. 5(a) and 5(b), a first pad 37 a and a second pad 37 bare formed on the upper insulation layer 35. The first pad 37 a isconnected to the current spreading layer 33 through the opening 35 a ofthe upper insulation layer 35, and the second pad 37 b is connected tothe reflective electrodes 30 through the openings 35 b of the upperinsulation layer 35. The first and second pads 37 a and 37 b may be usedas pads for connection of bumps for mounting the light emitting diode ona sub-mount, a package, or a printed circuit board, or pads for surfacemount technology (SMT).

The first and second pads 37 a and 37 b may be formed simultaneously bythe same process, for example, a photolithography and etching process ora lift-off process. The first and second pads 37 a and 37 b may includea bonding layer including, for example, Ti, Cr, Ni or the like, and ahigh conductivity metal layer including Al, Cu, Ag, Au or the like.

Then, the substrate 21 is divided into individual light emitting diodechips, thereby providing light emitting diode chips. The substrate 21may be subjected to a thinning process to have a thinner thicknessbefore being divided into the individual light emitting diode chips.

Hereinafter, the structure of a light emitting diode 100 according toone embodiment of the disclosed technology will be described in detailwith reference to FIG. 7.

The light emitting diode includes a substrate 21, a first conductivetype semiconductor layer 23, an active layer 25, a second conductivetype semiconductor layer 27, a first pad 37 a, and a second pad 37 b,and may further include reflective electrodes 30, a current spreadinglayer 33, a lower insulation layer 31, an upper insulation layer 35 andmesas M.

The substrate 21 may be or include a growth substrate for growth ofgallium nitride-based epitaxial layers, for example, a sapphiresubstrate, a silicon carbide substrate, or a gallium nitride substrate.The substrate 21 may include a first surface 21 a, a second surface 21b, and a side surface 21 c. The first surface 21 a is a plane on whichsemiconductor layers are grown, and the second surface 21 b is a planethrough which light generated in the active layer 25 is discharged tothe outside. The side surface 21 c connects the first surface 21 a tothe second surface 21 b. The side surface 21 c of the substrate 21 maybe perpendicular to the first surface 21 a and the second surface 21 b,without being limited thereto. Alternatively, the side surface 21 b ofthe substrate 21 may be inclined. For example, as indicated by a dottedline in FIG. 7, the substrate 21 may have an inclined side surface 21 dsuch that the first surface 21 a has a greater area than the secondsurface 21 b. In this embodiment, the substrate 21 may have a thickness(t1) of 225 μm to 400 μm.

The first conductive type semiconductor layer 23 is placed on the firstsurface 21 a of the substrate 21. The first conductive typesemiconductor layer 23 is continuous, and the active layer 25 and thesecond conductive type semiconductor layer 27 are placed on the firstconductive type semiconductor layer 23. The plural mesas M are placed tobe separated from each other on the first conductive type semiconductorlayer 23. As illustrated with reference to FIGS. 1(a) and 1(b), themesas M include the active layer 25 and the second conductive typesemiconductor 27 and have an elongated shape extending toward one side.Here, the mesas M are formed of a stack of gallium nitride compoundsemiconductor layers. As shown in FIGS. 1(a) and 1(b), the mesas M maybe placed within the first conductive type semiconductor layer 23. Forexample, the mesas M may be placed within an upper region of the firstconductive type semiconductor layer 23. Alternatively, as shown in FIG.6, the mesas M may extend to edges of the upper surface of the firstconductive type semiconductor layer 23 in one direction, whereby theupper surface of the first conductive type semiconductor layer 23 can bedivided into plural regions. With this structure, the light emittingdiode can relieve current crowding near corners of the mesas M, therebyfurther improving current spreading performance.

The reflective electrodes 30 are placed on the plural mesas M to formohmic contacts with the second conductive type semiconductor layer 27.As illustrated with reference to FIGS. 1(a) and 1(b), the reflectiveelectrodes 300 may include the reflective layer 28 and the barrier layer29, and the barrier layer 29 may cover an upper surface and a sidesurface of the reflective layer 28.

The current spreading layer 33 covers the plural mesas M and the firstconductive type semiconductor layer 23. The current spreading layer 33has or is placed to form openings 33 a respectively placed in upperregions of the respective mesas M such that the reflective electrodes 30are exposed therethrough. The current spreading layer 33 may cover theoverall area of the mesas M excluding some regions of the upper regionsof the mesas M in which the openings 33 a are formed, and may also coverthe overall area of the first conductive type semiconductor layer 23.The current spreading layer 33 also forms ohmic contacts with the firstconductive type semiconductor layer 23 and is insulated from the pluralmesas M. The current spreading layer 33 may include a reflective metalsuch as Al.

The current spreading layer 33 may be insulated from the plural mesas Mby the lower insulation layer 31. For example, the lower insulationlayer 31 may be interposed between the plural mesas M and the currentspreading layer 33 to insulate the current spreading layer 33 from theplural mesas M. In addition, the lower insulation layer 31 may have oris placed to form openings 31 b placed within the upper regions of therespective mesas M such that the reflective electrodes 30 are exposedtherethrough, and openings 31 a that expose the first conductive typesemiconductor layer 23 therethrough. The current spreading layer 33 maybe connected to the first conductive type semiconductor layer 23 throughthe openings 31 a. The opening 31 b of the lower insulation layer 31 hasa smaller area than the opening 33 a of the current spreading layer 33,and is completely exposed through the opening 33 a.

The upper insulation layer 35 covers at least a portion of the currentspreading layer 33. The upper insulation layer 35 has or is placed toform openings 35 b that expose the reflective electrodes 30. Inaddition, the upper insulation layer 35 may have or be placed to form anopening 35 a that exposes the current spreading layer 33. The upperinsulation layer 35 may cover sidewalls of the openings 33 a of thecurrent spreading layer 33.

The first pad 37 a may be placed on the current spreading layer 33 and,for example, may be connected to the current spreading layer 33 throughthe opening 35 a of the upper insulation layer 35. The first pad 37 a iselectrically connected to the first conductive type semiconductor layer23 through the current spreading layer 33. In addition, the second pad37 b is connected to the reflective electrodes 30 exposed through theopenings 35 b and electrically connected to the second conductive typesemiconductor layer 27 through the reflective electrodes 30.

According to this embodiment, since the substrate 21 has a thickness t1of 225 μm or more, the beam angle of the light emitting diode 100 can beincreased to 140° or more. Further, since the current spreading layer 33covers the mesas M and substantially cover the overall area of the firstconductive type semiconductor layer 23 between the mesas M, current canbe easily spread through the current spreading layer 33.

In addition, the current spreading layer 23 includes a reflective metallayer such as an Al layer or the lower insulation layer is formed as aninsulation reflective layer, whereby light not reflected by thereflective electrodes 30 can be reflected by the current spreading layer23 or the lower insulation layer 31, thereby improving light extractionefficiency.

FIG. 8 is a sectional view of a light emitting diode 200 according toanother embodiment of the disclosed technology.

The light emitting diode 200 according to this embodiment is generallysimilar to the light emitting diode 100 of FIG. 7 except for a conformalcoating 50 placed on the substrate 21. The conformal coating 50 coversthe second surface 21 b of the substrate 21 and may also cover the sidesurface 21 c of the substrate 21. The conformal coating 50 may have auniform thickness. The conformal coating 50 may contain a wavelengthconversion material such as phosphors.

Further, the sum of a thickness t1 of the substrate 21 and a thicknesst2 of the conformal coating 50 may range from 225 μm to 600 μm. Forexample, the conformal coating 50 may have a thickness t2 of 20 μm to200 μm. Further, the thickness t1 of the substrate 21 may vary dependingupon the thickness t2 of the conformal coating, for example, may rangefrom 150 μm to 400 μm.

When the sum (t1+t2) of the thickness t1 of the substrate 21 and thethickness t2 of the conformal coating 50 is greater than or equal to 225μm, the beam angle of the light emitting diode 200 can be increased to140° or more.

FIGS. 9 to 12 are graphs depicting beam angle characteristics of lightemitting diodes depending on thickness of substrates. In each of thegraphs, a solid line indicates beam angle characteristics in a firstaxis (for example, x-axis) and a dotted line indicates beam anglecharacteristics in a second axis (for example, y-axis) orthogonal to thefirst axis.

As the substrate 21, a sapphire substrate was used, and light emittingdiodes having the structure as shown in FIG. 7 were fabricated withdifferent thicknesses of the sapphire substrates 21. The light emittingdiodes had a size of 1 mm×1 mm and the sapphire substrates 21 hadthicknesses of about 80 μm, 150 μm, 250 μm, and 400 μm, respectively.

Referring to FIGS. 9 to 12, it can be confirmed that beam distributionwas widened by increasing thickness of the substrate 21 from 80 μm to250 μm. However, when the thickness of the substrate 21 was increasedfrom 250 μm to 400 μm, there was no significant difference in beamdistribution.

FIG. 13 is a graph depicting a relationship between beam angle andsubstrate thickness of the light emitting diodes that is obtained fromFIGS. 9 to 12. The term “beam angle” means the range of angles in whichluminous flux of half or more the maximum luminous flux is exhibited.The “beam angle” corresponds to an angle from a minimum angle to amaximum angle at which a normalized strength becomes 0.5 in a beamdistribution graph.

Referring to FIG. 13, as the thickness t1 of the substrate 21 wasincreased to 250 μm, the beam angle was increased to about 140°, andwhen the thickness t1 of the substrate 21 was 250 μm or more, there wasno significant change in the beam angle.

Accordingly, when the thickness t1 of the substrate 21 is set to 250 μm,the beam angle can be maintained at 140° without other transparent filmson the substrate 21, and there is no significant change in beam angleeven when the thickness t1 of the substrate 21 is increased.

FIGS. 14 to 17 are graphs depicting beam angle characteristics of lightemitting diodes 200 each having a conformal coating depending on varioussubstrate thicknesses (t1). In each of the graphs, a solid lineindicates beam angle characteristics in a first axis (for example,x-axis) and a dotted line indicates beam angle characteristics in asecond axis (for example, y-axis) orthogonal to the first axis.

As described with reference to FIGS. 9 to 12, sapphire substrates 21having different thicknesses t1 were used and a conformal coating 50 wasformed to a thickness t2 of about 75 μm on each of the substrates 21,thereby fabricating light emitting diodes 200, as shown in FIG. 8.

Referring to FIGS. 14 to 17, it can be confirmed that beam distributionwas significantly changed by increasing thickness of the substrate 21from 80 μm to 150 μm. In addition, as the thickness of the substrate 21was increased from 150 μm to 400 μm, there was no significant change inbeam distribution although luminous flux slightly decreases near 0°.

FIG. 18 is a graph depicting a relationship between beam angle andsubstrate thickness t1 of the light emitting diodes 200 that is obtainedfrom FIGS. 14 to 17, each of which includes the conformal coating 50.

Referring to FIG. 18, as the thickness t1 of the substrate 21 wasincreased to 150 μm, the beam angle was increased to about 143°, andwhen the thickness t1 of the substrate 21 was 150 μm or more, there wasno significant change in the beam angle. Thus, it can be seen that, whenthe sum of the thickness t1 of the substrate 21 and the thickness t2 ofthe conformal coating 50 reaches 225 μm or more, the beam angle finallyreaches a value of 140° or more.

Accordingly, when the sum of the thickness of the substrate 21 and thethickness of the conformal coating 50 is set to 225 μm or more, thelight emitting diode 200 can have a beam angle of 140° or more.

From the experimental results, it is anticipated that, even when thesubstrate has a thickness of about 225 μm without the conformal coating50, the light emitting diode 200 having a beam angle of 140° or morewill be provided.

FIGS. 19(a), 19(b), and 19(c) show schematic sectional views of a lightemitting diode module 300 a employing typical light emitting diodes 10and light emitting diode modules 300 b and 300 c employing lightemitting diodes 100 according to some implementations of the disclosedtechnology. Here, the light emitting diode modules 300 a, 300 b and 300c will be illustrated by way of example as being used in a backlightunit for illuminating a liquid crystal display panel 400.

Referring to FIGS. 19(a), 19(b), and 19(c), the typical light emittingdiode 10 has a beam angle (θ₁) of about 120°, whereas the light emittingdiode 100 according to some implementations of the disclosed technologyhas a beam angle (θ₂) of about 140° or more.

A distance between the light emitting diode module and the LCD panel 400can be represented by d, a pitch of the light emitting diodes can berepresented by p, and the beam angles of the light emitting diodes canbe represented by θ. On the other hand, when the light emitting diodesare arranged to prevent the beam angles of the light emitting diodesfrom overlapping each other, the pitch p indicates a width of an area ofthe LCD panel 400 illuminated by a single light emitting diode and isrepresented by the following Equation 1.p=2·d·tan(θ/2).  (Equation 1)

Thus, the pitch p1 of the typical light emitting diode module 300 a andthe pitch p2 of the light emitting diode module 300 b according to someimplementations of the disclosed technology are represented by Equations(2) and (3).p1=2·d1·tan(θ₁/2).  (Equation 2)p2=2·d2·tan(θ₂/2).  (Equation 3)

Here, since the beam angle (θ₂) of the light emitting diode 100 isgreater than the beam angle (θ₁) of the light emitting diode 10 and θ₂/2is less than 90°, the following Equation 4 is established.tan(θ₁/2)<tan(θ₂/2).  (Equation 4)

Accordingly, if d1=d2 in Equations 2 and 3, the following Equation 5 isestablished.p2>p1 (when d1=d2).  (Equation 5)

That is, when the light emitting diode modules 300 a and 300 b shown inFIGS. 19(a) and (b) are separated from the LCD panel 400 by the samedistance (d1=d2) and illuminate the same area of the LCD panel 400, thelight emitting diode module 300 b according to some implementations ofthe disclosed technology allows the light emitting diodes 100 to bearranged at wider intervals than the typical light emitting diode module300 a. Accordingly, it is possible to reduce the number of lightemitting diodes 100 included in the light emitting diode module 300 b.

On the other hand, as shown in FIGS. 19(a) and (c), when the pitch p1 ofthe light emitting diodes of the typical light emitting diode module 300a is the same as the pitch p3 of the light emitting diodes 100 of thelight emitting diode module 300 c according to some implementations ofthe disclosed technology, the following Equation 6 is established.d3<d1 (when p1=p3).  (Equation 6)

That is, when the light emitting diode modules 300 a and 300 c includethe same number of light emitting diodes, the light emitting diodemodule 300 c according to some implementations of the disclosedtechnology can be placed closer to the LCD panel 400 than the lightemitting diode module 300 a, thereby enabling reduction in thickness ofa backlight unit and a liquid crystal display.

Herein, although the light emitting diode modules 300 a, 300 b and 300 care illustrated as being used in the backlight unit, the light emittingdiode modules 300 a, 300 b and 300 c may also be used as a lightingmodule for lighting apparatuses. In this case, the lighting modules 300a, 300 b and 300 c can illuminate a diffusing plate 400 of a lightingapparatus, and, as described above, the light emitting modules accordingto some implementations of the disclosed technology can illuminate thesame area of the diffusing plate using a smaller number of lightemitting diodes, or allow the light emitting diodes to be placed closerto the diffusing plate than the typical light emitting module.

Next, a method of fabricating a light emitting diode will be describedto aid in understanding of the structure of a flip-chip type lightemitting diode according to another embodiment of the disclosedtechnology.

FIG. 20(a) through FIG. 24(b) are views illustrating a method offabricating a light emitting diode according to one embodiment of thedisclosed technology. In each figure, (a) shows a plan view and (b)shows a sectional view taken along line A-A.

First, referring to FIGS. 20(a) and 20(b), a first conductive typesemiconductor layer 123 is formed on a substrate 121, and an activelayer 125 and a second conductive type semiconductor layer 127 areplaced on the first conductive type semiconductor layer 123. Thesubstrate 121 is or includes a substrate for growth of GaN-basedsemiconductor layers and may be or include, for example, a sapphiresubstrate, a silicon carbide substrate, or a gallium nitride substrate.In some implementations, the substrate 121 may be or include a sapphiresubstrate. Although the substrate 121 may be provided in the form of alarge wafer capable of providing a plurality of light emitting diodes,FIGS. 20(a) and 20(b) show a portion of a substrate only for one offinal light emitting diodes after being separated from the plurality oflight emitting diodes. In the final light emitting diode, the substrate121 may have a parallelogram shape having an acute angle, for example, arhombus shape, without being limited thereto. Alternatively, thesubstrate may have any of a variety of polygonal shapes having an acuteangle, such as a triangular shape, a pentagonal shape, and the like.

The first conductive type semiconductor layer 123 may be or include anitride-based semiconductor layer doped with n-type impurities. In oneembodiment, the first conductive type semiconductor layer 123 may be orinclude an In_(x)Al_(y)Ga_(1-x-y)N layer (0≤x≤1, 0≤y≤1, 0≤x+y≤1) dopedwith Si. For example, the first conductive type semiconductor layer 123may be or include a Si-doped GaN layer. The second conductive typesemiconductor layer 127 may be or include a nitride-based semiconductorlayer doped with p-type impurities. In one embodiment, the secondconductive type semiconductor layer 127 may be or include anIn_(x)Al_(y)Ga_(1-x-y)N layer (0≤x≤1, 0≤y≤1, 0≤x+y≤1) doped with Mg orZn. For example, the second conductive type semiconductor layer 127 maybe or include a Mg-doped GaN layer. The active layer 125 may include awell layer including In_(x)Al_(y)Ga_(1-x-y)N (0≤x≤1, 0≤y≤1, 0≤x+y≤1) andmay have a single quantum well structure or a multi-quantum wellstructure. In one embodiment, the active layer 125 may have a singlequantum well structure including an InGaN, GaN or AlGaN layer, or amulti-quantum well structure including InGaN/GaN layers, GaN/AlGaNlayers, or AlGaN/AlGaN layers.

The first conductive type semiconductor layer 123, the active layer 125and the second conductive type semiconductor layer 127 may be formed bymetal organic chemical vapor deposition (MOCVD) or molecular beamepitaxy (MBE).

A mesa M may be formed on the first conductive type semiconductor layer123 and some region of the first conductive type semiconductor layer 123is exposed along an edge of the mesa M. As shown in FIGS. 20(a) and20(b), an upper surface of the first conductive type semiconductor layer123 may be exposed along an edge of the substrate 121 of the final lightemitting diode, and the active layer 125 and the second conductive typesemiconductor layer 127 may be placed within an upper surface of thefirst conductive type semiconductor layer 123.

The mesa may be formed by growing a semiconductor stack structure 126including the first conductive type semiconductor layer 123, the activelayer 125 and the second conductive type semiconductor layer 127 on afirst surface of the substrate 121 through metal organic chemical vapordeposition or the like, and patterning the second conductive typesemiconductor layer 127 and the active layer 125 so as to expose thefirst conductive type semiconductor layer 123. The mesa M may be formedto have an inclined side surface using photoresist reflow technology.The inclined profile of the side surface of the mesa M improvesextraction efficiency of light generated in the active layer 125. Inaddition, the mesa has a similar shape to the shape of the substrate 121in a plan view. For example, the mesa has at least one acute angle likethe substrate 121 in a plan view. The mesa may have a quadrangular shapeincluding a pair of obtuse angles facing each other and a pair of acuteangles facing each other in a plan view. The obtuse angles may have thesame value and the acute angles may have the same value. Such a planarshape of the mesa may be a rhombus shape or a diamond shape.

One side surface of the mesa may be perpendicular to a flat zone of thesubstrate 121. In one embodiment, when the substrate 121 is or includesa sapphire substrate, one side surface of the mesa may be aligned on anm-plane. The planar shape of the semiconductor stack structure 126 mayalso be similar to that of the mesa.

On the other hand, a reflective electrode 130 is formed on the secondconductive type semiconductor layer 127. The reflective electrode 130may be formed on the mesa M after the mesa M is formed, without beinglimited thereto. Alternatively, the reflective electrode 30 may beformed on the second conductive type semiconductor layer 127 beforeformation of the mesa M after growing the second conductive typesemiconductor layer 127. The reflective electrode 130 covers mostregions of an upper surface of the second conductive type semiconductorlayer and has substantially the same shape as the shape of the mesa M ina plan view.

The reflective electrode 130 includes a reflective layer 128 and mayfurther include a barrier layer 129. The barrier layer 129 may cover anupper surface and a side surface of the reflective layer 128. Forexample, the barrier layer 129 may be formed to cover the upper surfaceand the side surface of the reflective layer 128 by forming a pattern ofthe reflective layer 128, followed by forming the barrier layer 129thereon. For example, the reflective layer 128 may be formed bydeposition and patterning of Ag, Ag alloy, Ni/Ag, NiZn/Ag, or TiO/Aglayers. On the other hand, the barrier layer 129 may be formed toinclude Ni, Cr, Ti, or Pt or combinations thereof and prevents diffusionor contamination of metallic materials in the reflective layer 128.

After forming the mesa M, an edge of the first conductive typesemiconductor layer 123 may also be etched to expose the upper surfaceof the substrate 121. Here, the first conductive type semiconductorlayer 123 may also be formed to have an inclined side surface.

Referring to FIGS. 21(a) and 21(b), a lower insulation layer 131 isformed to cover the first conductive type semiconductor layer 123 andthe reflective electrode 130. The lower insulation layer 131 includes oris placed to form openings 131 a and 131 b at some portions of the lowerinsulation layer 131 to allow electrical connection to the firstconductive type semiconductor layer 123 and the reflective electrode 130therethrough. For example, the lower insulation layer 131 may include orbe placed to form openings 131 a which expose the first conductive-typesemiconductor layer 123 and an opening 131 b which expose the reflectiveelectrode 130.

The openings 131 a may be placed near edges of the substrate 121 aroundthe reflective electrode 130, and may have an elongated shape extendingalong the edges of the substrate 121. As shown in FIGS. 21(a) and 21(b),the openings 131 a are farther separated from one another at acute angleportions than at obtuse angle portions. With this structure, it ispossible to prevent current crowding near the acute angle portions. Inone embodiment, a distance between the openings 131 a near the acuteangle portion may be greater than or equal to a current spreadinglength, and a distance between the openings near the obtuse angleportion may be less than or equal to the current spreading length. Thecurrent spreading length means a length from an edge of a p-electrode toa place at which current density is decreased to 1/e times uponapplication of drive current.

On the other hand, the opening 131 b is placed in an upper region of thereflective electrode 130 and may be located towards the acute angleportion of the substrate 121. In one embodiment, the opening 131 b mayhave a triangular shape or a trapezoidal shape.

The lower insulation layer 131 may be formed to include oxides such asSiO₂, nitrides such as SiNx, or insulation materials such as MgF₂ bychemical vapor deposition (CVD) or the like. The lower insulation layer131 may be composed of a single layer or multiple layers. In addition,the lower insulation layer 131 may be formed as a distributed Braggreflector (DBR) in which low refractive material layers and highrefractive material layers are alternately stacked one above another.For example, an insulation reflective layer having high reflectivity maybe formed by stacking, for example, SiO₂/TiO₂ layers or SiO₂/Nb₂O₅layers.

In this embodiment, the openings 131 a exposing the first conductivetype semiconductor layer 123 have an elongated shape and are formedalong the edges of the substrate 121. However, other implementations arealso possible. For example, as shown in FIG. 25, a plurality of holes131 c exposing the first conductive type semiconductor layer 123 may bearranged along the edges of the substrate 121. In this case, theplurality of holes 131 c may be arranged to be farther separated fromone another around the acute angle portion than the obtuse angleportion, thereby relieving current crowding. In addition, a distancebetween the holes 131 c at opposite sides of the acute angle portion maybe greater than the distance between the holes 131 c at opposite sidesof the obtuse angle portion. In one embodiment, the distance between theholes 131 c at the opposite sides of the acute angle portion may begreater than or equal to the current spreading length, and the distancebetween the holes 131 c at the opposite sides of the obtuse angleportion may be less than or equal to the current spreading length. Theholes 131 c may have a polygonal shape, a circular shape, or asemi-circular shape.

Referring to FIGS. 22(a) and 22(b), a current spreading layer 133 isformed on the lower insulation layer 131. The current spreading layer133 covers the reflective electrode 130 and the first conductive typesemiconductor layer 123. In addition, the current spreading layer 133includes or is placed to form an opening 133 a, which is placed in theupper region of the reflective electrode 130 and exposes the reflectiveelectrodes 130. The current spreading layer 133 may form ohmic contactswith the first conductive-type semiconductor layer 123 through theopenings 131 a of the lower insulation layer 131. The current spreadinglayer 133 is insulated from the reflective electrode 130 by the lowerinsulation layer 131.

The opening 133 a of the current spreading layer 133 has a greater areathan the opening 131 b of the lower insulation layer 131 to prevent thecurrent spreading layer 133 from being connected to the reflectiveelectrode 130. Thus, the opening 133 a has sidewalls placed on the lowerinsulation layer 131.

The current spreading layer 133 is formed substantially over theentirety of the upper surface of the substrate 131 excluding the opening133 a. Accordingly, current can easily spread through the currentspreading layer 133. The current spreading layer 133 may include ahighly reflective metal layer such as an Al layer, and the highlyreflective metal layer may be formed on a bonding layer such as a Ti, Cror Ni layer. In addition, a protective layer having a single layer orcomposite layer structure including Ni, Cr, Au, and the like may beformed on the highly reflective metal layer. The current spreading layer133 may have a multilayer structure including, for example,Ti/Al/Ti/Ni/Au.

Referring to FIGS. 23(a) and 23(b), an upper insulation layer 135 isformed on the current spreading layer 133. The upper insulation layer135 includes or is placed to form an opening 135 a which exposes thecurrent spreading layer 133, and an opening 135 b which exposes thereflective electrode 130. The opening 135 a and the opening 135 b may bedisposed to face each other, and may be disposed near the acute angleportions of the substrate 121, as shown in FIG. 23(a). In addition, theopening 135 b exposes the reflective electrode 130, which is exposedthrough the opening 133 a of the current spreading layer 133 and theopening 131 b of the lower insulation layer 131. The opening 135 b has anarrower area than the opening 133 a of the current spreading layer 133.Accordingly, the sidewalls of the opening 133 a of the current spreadinglayer 133 may be covered by the upper insulation layer 135. On the otherhand, the opening 135 b may have a smaller area than the opening 131 bof the lower insulation layer 131. Alternatively, the opening 135 b mayhave a greater area than the opening 131 b of the lower insulation layer131. The opening 135 a may have a reversed trapezoidal shape and theopening 135 b may have a trapezoidal shape.

The upper insulation layer 135 may be formed using an oxide insulationlayer, a nitride insulation layer, or a polymer such as polyimide,Teflon, Parylene, or the like.

Referring to FIGS. 24(a) and 24(b), a first pad 137 a and a second pad137 b are formed on the upper insulation layer 135. The first pad 137 ais connected to the current spreading layer 133 through the opening 135a of the upper insulation layer 135, and the second pad 137 b isconnected to the reflective electrode 130 through the opening 135 b ofthe upper insulation layer 135. As a result, the first pad 137 a may beconnected to the first conductive type semiconductor layer 123 throughthe current spreading layer 133 and the second pad 137 b may beconnected to the second conductive type semiconductor layer 127 throughthe reflective electrode 130. The first and second pads 137 a and 137 bmay be used as pads for connecting bumps for mounting the light emittingdiode on a sub-mount, a package, or a printed circuit board, or pads forsurface mount technology (SMT).

The first and second pads 137 a and 137 b may be formed simultaneouslyby the same process, for example, a photolithography and etching processor a lift-off process. Each of the first and second pads 137 a and 137 bmay include a bonding layer including, for example, Ti, Cr, Ni or thelike, and a high conductivity metal layer including Al, Cu, Ag, Au orthe like. In addition, each of the first and second pads 137 a and 137 bmay further include a pad barrier layer covering the high conductivitymetal layer. The pad barrier layer prevents diffusion of metallicelements such as tin (Sn) in the course of bonding or soldering, therebypreventing increase in specific resistance of the first and second pads137 a, 137 b. The pad barrier layer may be formed of or include Cr, Ni,Ti, W, TiW, Mo, Pt or combinations thereof.

Then, the substrate 121 is divided into individual light emitting diodechips, thereby providing light emitting diode chips. For example, thesubstrate 121 may be divided into individual light emitting diode chipshaving a parallelogram shape by scribing along a group of m-planes. As aresult, a light emitting diode including the substrate 121, sidesurfaces of which are composed of or include the group of m-planes, canbe provided.

On the other hand, the substrate 121 may be subjected to a thinningprocess to have a thinner thickness before being divided into theindividual light emitting diode chips. Here, the substrate 121 may havea thickness of greater than 100 μm, for example, 225 μm to 400 μm.

On the other hand, a conformal coating 50 (see FIG. 27) may be furtherformed to cover the substrate 121 of the individual light emitting diodechip. The conformal coating 150 may be formed before or after thedivision of the substrate 121 into individual chips.

Hereinafter, the structure of a light emitting diode 100 a according toone embodiment of the disclosed technology will be described withreference to FIG. 26.

Referring to FIG. 26, the light emitting diode 100 a includes asubstrate 121, a first conductive type semiconductor layer 123, anactive layer 125, a second conductive type semiconductor layer 127, afirst pad 137 a, and a second pad 137 b, and may include a reflectiveelectrode 130, a current spreading layer 133, a lower insulation layer131 and an upper insulation layer 135.

The substrate 121 may be or include a growth substrate for growth ofgallium nitride-based epitaxial layers, for example, a sapphiresubstrate, a silicon carbide substrate, or a gallium nitride substrate.The substrate 121 may include a first surface 121 a, a second surface121 b, and a side surface 121 c. The first surface 121 a is a plane onwhich semiconductor layers are grown, and the second surface 121 b is aplane through which light generated in the active layer 125 isdischarged to the outside. The side surface 121 c connects the firstsurface 121 a to the second surface 121 b. The side surface 121 c of thesubstrate 121 may be perpendicular to the first surface 121 a and thesecond surface 121 b, but is not limited thereto. Alternatively, theside surface 121 b of the substrate 121 may be inclined. For example, asindicated by a dotted line in FIG. 26, the substrate 121 may have aninclined side surface 121 d such that the first surface 121 a has agreater area than the second surface 121 b.

In addition, the substrate 121 may have a polygonal shape including atleast one acute angle. For example, the first surface 121 a and thesecond surface 121 b may have a polygonal shape, such as a parallelogramshape, a triangular shape, a pentagonal shape, and the like, as shown inFIGS. 20(a) and 20(b). Since the substrate 121 includes an acute angle,the light emitting diode has improved light extraction efficiencythrough the acute angle portions while increasing the beam angle oflight at the acute angle portions.

In this embodiment, the substrate 121 may have a thickness of greaterthan 100 μm, for example, in the range of 225 μm to 400 μm. The beamangle of light can increase with the increase of thickness of thesubstrate 121, and when the substrate 121 has a thickness of 225 μm ormore, the beam angle of light can be generally maintained constant.

The first conductive type semiconductor layer 123 is placed on the firstsurface 121 a of the substrate 121. The first conductive typesemiconductor layer 123 may cover the overall surface of the firstsurface 121 a of the substrate 121, without being limited thereto.Alternatively, the first conductive type semiconductor layer 123 may beplaced within the substrate 121, for example, an upper region of thesubstrate, so as to allow the first surface 121 a to be exposed along anedge of the substrate 121.

A mesa including the active layer 125 and the second conductive typesemiconductor layer 127 is placed on the first conductive typesemiconductor layer 123. For example, the active layer 125 and thesecond conductive type semiconductor layer 127 are placed within thefirst conductive type semiconductor layer 127, for example, the upperregion of the first conductive type semiconductor layer 127, asdescribed with reference to FIGS. 20(a) and 20(b). Accordingly, someregion of the first conductive type semiconductor layer 127 may beexposed, for example, along the edge of the substrate 121.

The reflective electrode 130 forms ohmic contacts with the secondconductive type semiconductor layer 127. As described with reference toFIGS. 20(a) and 20(b), the reflective electrodes 130 include areflective layer 128 and a barrier layer 129, which may cover an uppersurface and a side surface of the reflective layer 128.

The current spreading layer 133 covers the reflective electrode 130 andthe first conductive type semiconductor layer 123. The current spreadinglayer 133 has or is placed to form an opening 133 a placed in an upperregion of the reflective electrode 130 such that the reflectiveelectrode 130 is exposed through the opening. The current spreadinglayer 133 may cover the overall area of the reflective electrode 130excluding a portion of the upper region of the reflective electrode 130in which the opening 133 a is formed, and may also cover the overallarea of the first conductive type semiconductor layer 123.

The current spreading layer 133 also forms ohmic contacts with the firstconductive type semiconductor layer 123 and is insulated from thereflective electrode 130. For example, the current spreading layer 133may be insulated from the reflective electrode 130 by the lowerinsulation layer 131. The lower insulation layer 131 is placed betweenthe reflective electrode 130 and the current spreading layer 133 toinsulate the current spreading layer 133 from the reflective electrode130.

In addition, the lower insulation layer 131 may have an opening 131 bplaced within the upper region of the reflective electrode 130 such thatthe reflective electrode 30 is exposed therethrough, and openings 131 athat expose the first conductive type semiconductor layer 123therethrough. The opening 131 b of the lower insulation layer 131 has asmaller area than the opening 131 a of the current spreading layer 133and is completely exposed through the opening 133 a.

On the other hand, the current spreading layer 133 may be connected tothe first conductive type semiconductor layer 123 through the openings131 a. Here, as described with reference to FIGS. 21(a) and 21(b), theopenings 131 a may be placed along edges of the substrate 121 and may befarther separated from each other around an acute angle portion thanaround an obtuse angle portion. With this structure, the light emittingdiode can prevent current crowding at the acute angle portion, therebyimproving luminous efficacy. In addition, the lower insulation layer 131may include holes 131 c as described with reference to FIG. 25, insteadof the openings 131 a.

The upper insulation layer 135 covers at least a portion of the currentspreading layer 133. In addition, the upper insulation layer 135 has oris placed to form an opening 135 a that exposes the current spreadinglayer 133 and an opening 135 b that exposes the reflective electrode130. The opening 135 a and the opening 135 b may be placed near theacute angle portions to face each other. In addition, the upperinsulation layer 135 may cover a sidewall of the opening 133 a of thecurrent spreading layer 133, and the opening 135 b may be placed withinthe opening 133 a.

The first pad 137 a may be placed on the current spreading layer 133and, for example, may be connected to the current spreading layer 133through the opening 135 a of the upper insulation layer 135. The firstpad 137 a is electrically connected to the first conductive typesemiconductor layer 123 through the current spreading layer 133. Inaddition, the second pad 137 b is connected to the reflective electrode130 exposed through the opening 135 b and electrically connected to thesecond conductive type semiconductor layer 127 through the reflectiveelectrode 130.

According to this embodiment, the substrate 121 has a polygonal shapeincluding at least one acute angle, such as a parallelogram shape or atriangular shape, thereby improving light extraction efficiency.Furthermore, luminous flux through the acute angle portions isincreased, whereby the beam angle of the light emitting diode can beadjusted using the acute angle portions.

In addition, according to this embodiment, the substrate 121 has athickness of 100 μm or more, thereby improving the beam angle of light.

Further, the current spreading layer 123 includes a reflective metallayer such as an Al layer or the lower insulation layer is formed as aninsulation reflective layer, whereby light not reflected by thereflective electrodes 130 can be reflected by the current spreadinglayer 123 or the lower insulation layer 131, thereby improving lightextraction efficiency.

FIG. 27 is a sectional view of a light emitting diode 200 a according toyet another embodiment of the disclosed technology.

The light emitting diode 200 a according to this embodiment is generallysimilar to the light emitting diode 100 a of FIG. 26 except for aconformal coating 150 placed on the substrate 121. The conformal coating150 evenly covers the second surface 121 b of the substrate 121 and mayalso cover the side surface 121 c. The conformal coating 150 may containa wavelength conversion material such as phosphors.

Further, the sum of the thickness of the substrate 121 and the thicknessof the conformal coating 150 may be 225 μm to 600 μm. For example, theconformal coating 150 may have a thickness of 20 μm to 200 μm. Further,the thickness of the substrate 121 may vary depending upon the thicknessof the conformal coating, for example, may range from 100 μm to 400 μm.When the sum of the thickness of the substrate 121 and the thickness ofthe conformal coating 150 is greater than or equal to 225 μm, the beamangle of the light emitting diode 200 a can be increased to 140° ormore.

FIGS. 28(a) and 28(b) show schematic plan views illustrating lightextraction characteristics depending on the shape of a substrate. Here,(a) shows a travelling passage of light in a typical substrate 111having a rectangular shape, and (b) shows a traveling passage of lightin a substrate 121 having a diamond shape including acute anglesaccording to one embodiment of the disclosed technology.

Referring to FIG. 28(a), some of light generated at a specific place Lpin an active layer enters the substrate 111 and repeats total reflectionon inner side surfaces of the substrate 111. As a result, the lighttravels a substantial distance within the substrate 111, thereby causinglight loss within the substrate 111. As the thickness of the substrate111 increases, total reflection of light becomes more severe on the sidesurfaces of the substrate 111, thereby increasing light loss.Furthermore, since light emitted from portions of the substrate 111 hassimilar characteristics, there is no substantial difference in beamangle according to directions.

On the contrary, in the substrate 121 having a diamond shape as shown inFIG. 28(b), some of light generated at a specific place Lp in an activelayer enters the substrate 121, is totally reflected by inner sidesurfaces of the substrate 121, and then discharged outside with areduced incidence angle of light near an acute angle portion.Accordingly, as compared with the typical substrate 111, the substrate121 having a diamond shape provides improved light extractionefficiency. Furthermore, since light extraction efficiency is increasedat the acute angle portion, the beam angle of light increases at theacute angle portion as compared with the obtuse angle portion.Accordingly, it is possible to provide a light emitting diode havingdifferent beam angles depending on directions.

FIG. 29 is graph depicting beam angles of a flip-chip type lightemitting diode fabricated by a typical method and a flip-chip type lightemitting diode fabricated by a method according to one embodiment of thedisclosed technology. In the light emitting diode fabricated by thetypical method, a substrate 111 had a rectangular shape of 300 μm×1000μm and a thickness of about 250 μm. In the flip-chip type light emittingdiode fabricated by the method according to the embodiment, a distancebetween acute angle portions of a substrate 121 was 1 mm and a distancebetween obtuse angle portions thereof was about 0.58 mm.

Referring to FIG. 29, for the typical light emitting diode, a beam angledistribution (R-X) in the x-axis (minor axis) direction is generallysimilar to a beam angle distribution (R-Y) in the y-axis (major axis)direction. On the contrary, for the light emitting diode according tothe embodiment of the disclosed technology, a beam angle distribution(D-Y) in the x-axis direction passing the acute angle portions isgreater than a beam angle distribution (D-X) in the y-axis directionpassing the obtuse angle portions.

Thus, according to the embodiments of the disclosed technology, it ispossible to provide a light emitting diode exhibiting different beamangle characteristics according to the x-axis direction and the y-axisdirection. Such a light emitting diode may be advantageously used in alighting apparatus, which requires different beam angle characteristicsdepending on direction, such as an LED fluorescent lamp. For example, aplurality of light emitting diodes may be linearly arranged to beperpendicular to the longitudinal direction of the LED fluorescent lamphaving a wide beam angle, thereby enabling illumination of a wide areawhile reducing light loss within the fluorescent lamp.

Only a few embodiments, implementations and examples are described andother embodiments and implementations, and various enhancements andvariations can be made based on what is described and illustrated inthis document.

What is claimed is:
 1. A light emitting diode apparatus, comprising: aprinted circuit board; a display panel spaced from the printed circuitboard by a first distance (d); and light emitting diode units disposedon the printed circuit board to illuminate a corresponding area of thedisplay panel, the light emitting diode units spaced from one another bya second distance (p) and having a beam angle θ of 140° or more towardsthe display panel, and wherein the second distance is determined by anequation, p=2·d·tan(θ/2), and wherein at least one of the light emittingdiode units includes: a transparent substrate having a first surface, asecond surface, and a side surface connecting the first surface and thesecond surface; a first conductive type semiconductor layer placed onfirst surface of the transparent substrate and contacting the firstsurface of the transparent substrate; a second conductive typesemiconductor layer placed on the first conductive type semiconductorlayer; an active layer placed between the first conductive typesemiconductor layer and the second conductive type semiconductor layerand operable to emit light in response to an electrical current throughthe first and second conductive type semiconductor layers; and a lowerinsulation layer covering upper surfaces of the first conductive typesemiconductor layer, the lower insulation layer including a plurality ofopenings exposing a surface of the first conductive type semiconductorlayer and extending along the side surface of the transparent substrate;wherein the first conductive type semiconductor layer is structured toexpose the first surface of the transparent substrate at a region wherethe first surface is connected to the side surface.
 2. The lightemitting diode apparatus of claim 1, wherein the first distance is afunction of a thickness of the display panel.
 3. The light emittingdiode apparatus of claim 1, wherein a number of the light emitting diodeunits to illuminate the area of the display panel is a function of thesecond distance.
 4. The light emitting diode apparatus of claim 1,wherein at least one of the light emitting diode units further includes:a first pad electrically connected to the first conductive typesemiconductor layer; and a second pad electrically connected to thesecond conductive type semiconductor layer.
 5. The light emitting diodeapparatus of claim 1, further comprising a conformal coating layerincluding a phosphor covering the side surface of the transparentsubstrate from the first surface to the second surface and does notextend beyond the first surface of the transparent substrate.
 6. Thelight emitting diode apparatus according to claim 5, wherein theconformal coating layer has a thickness of 20 μm to 200 μm.
 7. The lightemitting diode apparatus of claim 1, further comprising a currentspreading layer contacting an edge of the first conductive typesemiconductor layer and formed on a portion of an area above the secondconductive type semiconductor layer.
 8. The light emitting diodeapparatus of claim 4, wherein the plurality of openings includes a firstopening and a second opening, and the second pad is formed over a regionbetween the first opening and the second opening.
 9. The light emittingdiode apparatus according to claim 1, wherein the transparent substratehas a thickness of 150 μm to 400 μm.
 10. The light emitting diodeapparatus of claim 1, wherein the plurality of openings exposes acurrent spreading layer to the first conductive type semiconductorlayer.
 11. The light emitting diode apparatus of claim 1, wherein adistance between the plurality of openings increases at an angledportion of the transparent substrate.
 12. A light emitting diodeapparatus comprising: light emitting diode units structured toilluminate an area located at a first distance (d) from the lightemitting diode units, each light emitting diode unit having a beam angleθ of 140° or more towards the area and including a transparentsubstrate, a first conductive type semiconductor layer placed on a firstsurface of the transparent substrate and contacting the first surface ofthe transparent substrate, a second conductive type semiconductor layerplaced on the first conductive type semiconductor layer, an active layerplaced between the first conductive type semiconductor layer and thesecond conductive type semiconductor layer and operable to emit light inresponse to an electrical current through the first and secondconductive type semiconductor layers, a lower insulation layer coveringupper surfaces of the first conductive type semiconductor layer and thesecond conductive type semiconductor layer, a first pad electricallyconnected to the first conductive type semiconductor layer, and a secondpad electrically connected to the second conductive type semiconductorlayer, wherein the light emitting diode units are spaced apart from oneanother by a second distance (p) that is a function of the beam angle θ,and the first conductive type semiconductor layer is structured toexpose the first surface of the transparent substrate at a region wherethe first surface is connected to the side surface of the transparentsubstrate, and wherein the lower insulation layer includes a pluralityof openings exposing a surface of the first conductive typesemiconductor layer and extending along a side surface of thetransparent substrate.
 13. The light emitting diode apparatus of claim12, wherein the second distance (p) is determined by an equationp=2·d·tan(θ/2).
 14. The light emitting diode apparatus of claim 12,wherein a number of the light emitting diode units to illuminate thearea is a function of the second distance.
 15. The light emitting diodeapparatus of claim 12, wherein the transparent substrate has a secondsurface and the side surface connects the first surface and the secondsurface.
 16. The light emitting diode apparatus of claim 15, furthercomprising a conformal coating layer including a phosphor covering theside surface of the transparent substrate from the first surface to thesecond surface and does not extend beyond the first surface of thetransparent substrate.
 17. The light emitting diode apparatus accordingto claim 16, wherein the conformal coating layer has a thickness of 20μm to 200 μm.
 18. The light emitting diode apparatus of claim 12,further comprising a current spreading layer contacting an edge of thefirst conductive type semiconductor layer and formed on a portion of anarea above the second conductive type semiconductor layer.
 19. The lightemitting diode apparatus of claim 12, wherein the plurality of openingsincludes a first opening and a second opening and the second pad isformed over a region between the first opening and the second opening.20. The light emitting diode apparatus according to claim 12, whereinthe transparent substrate has a thickness of 150 μm to 400 μm.